Transducers, sensors and other like instruments are frequently coupled to the end of long cables and inserted into well holes (such as those drilled into an aquifer for the production of water). (As used in the specification and the Claims to follow, the term "transducer" shall include, without limitation, transducers, sensors, and other like instruments used to obtain the measurement of one or more parameters from the surrounding environment.) For example, it is useful to know how the pressure near the bottom of a well varies over long periods of time because such variations can be used to determine fluctuations in the level of an aquifer.
Generally, the cable comprises one or more insulated conductors, usually surrounded by a braided metallic shielding, all of which are encased in an insulating jacket. In addition, a hollow vent tube may be inserted through the center of the cable to maintain the lower end of the cable at atmospheric pressure. Furthermore, a filler material, such as Kevlar, may be used inside the shielded braid and between the insulated conductors. A waterproof, pressure tight transducer, such as a pressure sensor, can be coupled in a water tight manner to the conductors at the end of the cable. The Kevlar fibers, running the entire length of the cable, absorb strain on the cable when it is raised or lowered and prevent the cable from stretching so much that the conductor wires are pulled from their connection with the transducer.
When a transducer and cable are lowered into a well, the insulating jacket may be subjected to abrasion, sharp well casing edges and joints, and sharp rocks if no casing is used, any of which may cause the cable jacket to be pierced, ripped or otherwise opened. As a result, water or other fluids may enter the cable, travel through the interior of the cable and leak into the transducer housing where the electrical and mechanical elements found there can be damaged or destroyed.
It is also known that fluid will seep through an insulating jacket which has been left in the fluid, such as water, for a long period of time. Thus, even if the jacket is not physically damaged during repeated lowering and raising operations, if the cable is left in place on a long term or permanent basis, the fluid will eventually seep into the interior of the cable and travel through the cable and into the transducer housing where damage can occur.
Known sealing methods are generally directed toward preventing water from entering the transducer housing at the point where the cable enters the housing. For example, U.S. Pat. No. 4,533,418, issued to Appling on Aug. 6, 1985, discloses a method of bonding a metal termination member to an electrical cable which has an internal armor layer and an external polyurethane jacket. The external jacket is split longitudinally and peeled away from the cable. The electrical wires of the cable are connected to the termination member as is the armor layer. The armor layer is then primed with a thermoplastic adhesive which adheres to both metal and polyurethane, and the split jacket repositioned over the cable and termination member. The entire assembly is then heated and compressed such that the polyurethane jacket flows sufficiently to bond the split halves together and to the termination member.
A disadvantage of such a method is that it will not prevent water which enters the cable above the bonding area from traveling through the interior of the cable into the termination member. Furthermore, it can only be used with an insulating jacket made of a flowable material such as polyurethane. It cannot easily be used with a more modern jacket material, Teflon, which melts at a much higher temperature than polyurethane and which has the advantage of being chemically inert.
U.S. Pat. No. 4,484,022, issued by Eilentropp on Nov. 20, 1984, discloses a method of making tensile-, pressure- and moisture-proof connections. To connect two insulated wires, a length of insulation is removed from the end of each wire and the exposed conductors are placed in opposite ends of a metal conductor sleeve. The connected wires and conductor sleeve fit inside an annular element (such as another sleeve) and a somewhat smaller, annular preformed filler is inserted in the annular element around the wires and conductor sleeve. Annular plungers surrounding the wires are inserted into each end of the annular element and the entire apparatus is heated causing the filler to melt. When the plungers are pressed into the annular element, they compress the melted filler causing it to flow and fill all of the empty spaces inside the annular element. According to the disclosure, the resulting connection, when cooled, provides a waterproof seal. In a similar fashion, the disclosed method can be used for terminating electrical conductors; a single plunger would be used instead of two.
The foregoing method does not utilize a sealant injection technique. Nor does it require that the sealant be injected along the conductors and past the sleeve.
Also known are methods whereby a liquid material is injected through the insulating jacket at numerous points along the cable and the material, when hardened or cured, becomes a water or pressure barrier inside of the cable. For example, U.S. Pat. No. 3,290,194,issued to Gillemont on Dec. 6, 1966, discloses a process and apparatus for injecting fluids into a sheathed cable. To use the device, a portion of the outer covering of the cable is removed, preferably around the entire circumference at the point at which the injection is to occur. It is also suggested that portions from the interior of the cable, such as metal sheath, be removed to expose the cable core. A nozzle is inserted into the opening and the device secured in place. The desired sealing fluid is then injected into the interior of the cable and the fluid allowed to harden. Once the source of the fluid is disconnected from the nozzle, the nozzle is left in place and its opening capped to prevent fluid from leaking back out.
Such a method and apparatus present an obvious disadvantage in that the cable sheath is breached, in this case, partially removed, thereby creating an opportunity for eventual water invasion. The nozzle of the Gillemont patent remains in place with at least a portion remaining attached to the exterior of the cable. This may present difficulties in lowering and raising the cable into and out of a hole and, further, such projections may have a tendency to become caught in a well hole with resulting damage to the cable or the seal. Furthermore, if a two-part sealant is used, air bubbles tend to form when the two parts are mixed. If the bubbles are not removed prior to injection (such as by applying a vacuum to the sealant), they will reduce the effectiveness of the plug. Finally, the use of Teflon sheathing, because of its non-adhesive properties, may prevent a watertight seal where the device is secured.
Consequently, a need has arisen for providing a seal internal to the cable which prevents fluid from infiltrating into a transducer body through the interior of the cable.